This might be a straight forward answer, and I know that you don't have to set NSObject as the Superclass when creating a new class.
But say, for example, I wanted to create a class which held a set of custom CABasicAnimations. Although it may be perfectly ok for me to use CABasicAnimation as the superclass, is it recommended that I follow the unwritten rule and still use NSObject or would you, if you were writing such a class, use CABasicAnimation as the Superclass?
I would assume that it wouldn't matter as long as the Class only contained properties and methods relative to CABasicAnimation.
It would be interesting to here your thoughts!
The rule is to subclass whatever object you are trying to extend. NSObject is used for many subclasses because it is the root object, but if I was going to write a class that was very similar to NSTableView, then I would subclass NSTableView.
In your case, if you are writing a custom animation that you want to call, then you should consider subclassing from CABasicAnimation. On the other hand, if you animation is really just a collection of pre-exisiting CA animations, then NSObject would be fine.
a class which held a set of custom CABasicAnimations.
In this case, I'd like to use Category instead of Subclass.
Related
I'm creating multiple different UI subclasses which can be created using JSContext, and I'd like them all to inherit a certain set of methods.
The classes vary from NSButton to NSTextView. It would be nice to have a single subclass act as NSView parent class, but I can't figure out if this is possible — or how to begin searching.
For example:
#interface CustomButtonClass : NSButton
I'm looking for a way to make NSButton inherit from a custom NSView subclass.
Is there a way to go around this, or do I need to create multiple intermediate classes?
The answer was super obvious, but coming from different languages, I struggled to make the connection. Thanks to all the comments, it was super easy to figure out.
Rather than trying to insert an intermediate class somewhere in the inheritance tree, you can create a category for NSView. Categories can also include all the required protocols.
For example, in my case, I wanted to expose multiple NSView methods to JSContext, and create some of my own, which would work on any NSView-derived object.
#protocol JSInterfaceExports <JSExport>
// Anything you want to expose to JS
- (void)customMethod;
// You can also expose all the common NSView properties
// and methods to JS in this protocol
#property (nonatomic) NSRect frame;
- (void)removeFromSuperview;
#end
#interface NSView (JSInterface)
// Any custom methods and properties
- (void)customMethod;
#end
Include this file on any NSView subclass, make them comply to <JSInterfaceExports>, and you are set.
So my question is: How to make a reference to a UIViewController from an outside ObjectiveC class. I have a ViewController, and a UIScrollView on it, and a class that needs to override some methods, and eventually return said UIScrollView. So, i figured that the easiest way to do this is to type:
return destinationViewController.scrollView;
but i don't quite know how to make the destinationViewController reference. Help?
You should be able to pass it as a parameter to the outside class, otherwise you should rethink your class design. In worst case, you can store it in AppDelegate or some specialized singleton (or public static field (like static UIViewController *g_ViewController) in the worst worst case)...
I have a two different ways of representing data in my app: via UITableView or UIScrollView.
So I have 2 main classes: AppTableView: UITableView and AppScrollView: UIScrollView.
And I want to implement the same additions to both views. So I wrote two classes: SomeAdditionsTableView: UITableView and SomeAdditionsScrollView: UIScrollView. The code of this classes is the same.
Main classes now looks like
AppTableView: SomeAdditionsTableView and AppScrollView: SomeAdditionsScrollView.
How to avoid this code duplicate? Thanks in advance.
Yeah this is a problem with the lack of multiple inheritance in Objective-c. I had the same problem when needing certain methods on a subclass of UIView and UIScrollView separately here: Subclassing UIView vs UIScrollView. There are 3 possible solutions I know of:
If you don't need to store any kind of instance variable, simply declare a category on UIScrollView and make sure to import that category into the two subclasses. This is the easiest solution, but least likely to work since you probably need to store state information if you're subclassing anyway.
Only create a subclass of UITableView and simply don't use it as a UITableView when you don't want a UITableView. You can technically just use a UITableView as a UIScrollView without invoking any of the tableView's methods. Of course, you're going to end up carrying around the 'weight' of a tableView (all of it's instance variables) but there no reason you have to use a UITableView as a UITableView and not just a UIScrollView.
Delegate as much of your code to a separate object to minimize code duplication. In each separate subclass carry an instance variable that is the method delegate and forward method calls to that delegate. Now here's where it gets fun. You can use protocols to declare the delegate methods in your subclass and override a special NSObject method: - (id) forwardingTargetForSelector:(SEL)aSelector to make sure those method calls get sent to the delegate. You use a category on the subclass that conforms to the protocol declared in the delegate class. This will expose all the methods of the delegate class in the subclass without requiring you to actually implement those methods in the subclass. When the runtime can't find the declared method in the subclass, it will call - (id) forwardingTargetForSelector:(SEL)aSelector, which you can use to return your delegate/forwarded class. This will prevent you from needing forward each individual method. Depending on what those method calls do, this may take a little more 'wiring', but it'll save you a lot of code writing in the end. It essentially 'mimics' multiple inheritance in objective-c using protocols. See my question/answer here for more details: https://stackoverflow.com/a/9419587/1147934.
Of the three, the last option tends to work the best for me. It takes a little work to get your head around but will significantly reduce code duplication. I also use it when I want to subclass without subclassing. The biggest requirement, though, is any class that you want to do this with will have to move it's method declarations out of it's interface into a separate protocol. But it's really not a big deal and the benefits of getting 'multiple inheritance like behavior' is great.
Also, there are times you may need the forwarded class to access instance variables in the forwarding class (the subclass). You can achieve this by using a delegate pattern whereby the forwarded class maintains a weak reference to the forwarding class in order to access those instance variables. For example, in your case, if you're trying to delegate methods that operate on a UIScrollView, those methods may need to be able to access that view. If those methods are stuck in a delegate class, they won't have direct access to the view's variables unless you give it to them. As usual with any delegate pattern, be very careful you don't create a retain cycle.
If your additions don't need any state of their own, you can make them a category on UIScrollView. Then, since a UITableView is a type of UIScrollView, you can use the category methods on one of those too.
If they do need to define new variables, then I would make it an independent class and have a MyTableView : UITableView subclass with a SomeAdditions property and, similarly, MyScrollView : UIScrollView.
You can achieve a lot by using protocols and "has_a"-relationships, instead of inheritance's "is_a"-relationships.
One very common pattern is delegate, but protocols are also useful for forwarding methods calls to encapsulated or wrapped objects.
in the following example to classes, that are not related to each other, share a common object, but it is also possible, that objects of the same kind use objects of different classes, that all implement a common protocol, so equal objects could do very different stuff.
#interface ClassA : NSObject
#property (strong) id<BrainProtocol> *brain
#end
##implementation ClassA
#synthezise brain;
-(void)theMethod
{
[brain theMethod];
}
#end
#interface ClassB : NSObject
#property (strong) id<BrainProtocol> *brain
#end
##implementation ClassB
#synthezise brain;
-(void)theMethod
{
[brain theMethod];
}
#end
ClassA *a = [[ClassA alloc] init];
ClassB *b = [[ClassB alloc] init];
//A object, that implements the BrainProtocol
Brain *brain = [[brain alloc] init];
[a setBrain:brain];
[b setBrain:brain];
The question is not only regarding the headline, but more of a "how will I achieve this, without trying to force a Java/Flash design into an Objective C (iPhone)program".
I have 6 views that extends UIView, these views all have different behavior but share certain methods, like -(void) update and -(void) changeState:(NSInteger)state.
A viewController, whose job is it to update, instantiate and display these views has a switch block to do this. So switch(4) {...} instantiates UIView4, but as I need a reference to the currently instantiated view (to do update and changeState:), I have a UIView property on my ViewController called self.currentView. As the instantiated UIView4 extends UIView I can easily go [self.currentView addSubview:UIView4instance] and then release the UIView4instance.
Now how will I call the [UIView4instance update] method on the view? or the [UIView5instance changeState] etc. etc.
Since I added it to self.currentView which is of type UIView it no longer has any reason to believe it has an update or changeState: method, meaning I cannot iterate the views and send them these messages.
This approach brings on a ton of other problems, I would need to test and typeCast my views each time I needed to do any operations on them.
If I were doing something like this Composite Pattern approach in, say, Java. I would either write an interface that all the views (UIView1, UIview2.... UIViewN) would implement. Or maybe an abstract class that all the views inherited the changeState: and update methods from.
This way I could have self.currentView just know that I'm adding objects to your view and they all conform to these methods.
The two solutions I can think of, with my very small Objective-C experience is:
doing it with delegation or categories, but this seems overkill in every way :/
I guess I could also extend UIView and then extend my class extending UIView again, but there is probably a reason Objective-C does not directly support abstract classes...
Hope someone could point me in the right direction regarding these issues.
Thanks:)
Yes it is equal. You can declare a protocol
#protocol MyViewProtocol
-(void)update;
-(void)changeState:(NSInteger)state;
#end
and declare your subclasses like
#interface MyUIView3 : UIView<MyViewProtocol> {
....
}
....
#end
Then, the declaration
UIView<MyViewProtocol>* view=[[MyUIView3 alloc] init];
means that view is an instance (of a subclass of) UIView which also conforms to MyViewProtocol.
Just the way it works in Java, I think. See the apple doc on protocols.
One thing to be aware of is that while defining a protocol like this is a convenience and certainly makes things clearer, it is by no means necessary to make your solution work. Objective-C binds methods at runtime, and so all you really need to do is to make sure all your view classes implement the methods you care about and call them.
You will get a complier warning for this, but it will work.
Now, in general it's probably preferable to define a protocol like this and it's what I generally do. But it's also important to remember that runtime binding is there and can be incredibly powerful.
In Objective-C, how do you rewire a class's instance method to call a method in another class?
Say a UIView class A contains another UIView class called childA. I want it so that when childA's drawRect is called, a method in class A is invoked without having to subclass childA and do the desired call in its drawRect there. How can this be achieved?
Also, how do I supply a method to childA's draw class dynamically? I know this is probably not a good practice but it would be useful for testing purposes.
To answer your first question about rewiring methods:
You don't want to be doing this on general principle, since it kinda defeats the whole purpose of object-oriented design, but for testing purposes, it can be useful. As long as you're on Leopard, it's not especially difficult, either.
Take a look at the Objective-C 2.0 Runtime Reference, which contains the keys to the kingdom, as it were. Look at the functions class_getInstanceMethod, method_getImplementation, method_getTypeEncoding, and class_addMethod which, in combination, let you change the methods of a class at runtime.
If you're just swizzling one selector for another, method_exchangeImplementations is a useful shortcut.
To answer your second question about supplying a method dynamically, that's as simple as passing a SEL to a method and then calling -performSelector:withObject::
#interface MyView : NSView {
SEL drawingSelector;
id drawingDelegate;
}
#property SEL drawingSelector;
#property id drawingDelegate;
#end
#implementation MyView
- (void)drawRect:(NSRect)rect {
[self.drawingDelegate performSelector:drawingSelector withObject:[NSValue valueWithRect:rect]];
}
#end
For the first issue you raise, it seems like you would set up UIView A as a delegate object of childA and the other UIViews - then they could use delegate methods to call the extra drawing features you wanted in A.
Either that or have each child ask for the superview and if it is of type "A" call the method you are interested in.